1. Field of the Invention
The present invention relates to an optically-active compound having a 1,1′-binaphthalene ring structure and a polymerizing group, to a liquid-crystal composition containing it, to a polymer obtained by polymerizing the optically-active compound or the liquid-crystal composition, and to use of the polymer. The polymer can be utilized for shaped articles of optical anisotropy, polarizers, optical compensators, brightness-improving films, orientation films, color filters, holographic devices, liquid-crystal display devices, adhesives, synthetic polymers of mechanical anisotropy, cosmetics, decorations, forgery-preventing devices, non-linear optical devices, and optical memory devices that are containing the shaped articles, etc.
2. Description of the Related Art
Polymerizing liquid-crystalline compounds are utilized these days for shaped articles of optical anisotropy. They have optical anisotropy in a liquid-crystal condition, and their orientation is fixed through polymerization.
When an optically-active compound is added to a polymerizing liquid-crystal composition, then it induces a helical structure. Depending on the helical pitch, the composition may have various applications for optical devices. Specifically, the light propagation along the helical axis is grouped into applications in a case of (1) λ much smaller than P (λ<<P) and in a case of (2) λ nearly equal to P (λ≈P), depending on the intended wavelength (λ) and the helical pitch length (P).
When the intended λ is corresponding to visible light, then the case (1) λ<<P corresponds to 1 (μm)<P. The application of this case is further grouped into a case satisfying the Morgan condition and a case not satisfying it. (A) When the Morgan condition is satisfied, or that is, when Φ<<2πΔnd/λ is satisfied, then the linearly-polarized light that is parallel to or perpendicular to the optical axis direction on the light incident side directly goes out as it is the linearly-polarized light, and functions as a rotator. In this, Φ indicates the total twist angle, d indicates the thickness, and Δn indicates the birefringence of liquid crystal. (B) When the Morgan condition is not satisfied, then the linearly-polarized light shows birefringence to be determined by Φ, d and Δn.
The rotator may be applied to optical devices for head-up displays or projectors. The twist-oriented birefringence application is, for example, for optical compensation in STN (Super-Twisted Nematic) liquid-crystal displays (see Patent Reference 1).
When the intended λ is corresponding to visible light in the case (2) λ≈P, and for example, when the twisted direction of the helical structure is in the right-handed direction, then the liquid-crystal film may selectively reflect only the right-handed circularly-polarized light having a wavelength λ within a range of no×P<λ<ne×P (where no indicates the ordinal refractive index of the liquid-crystal layer; and ne indicates the extra-ordinal refractive index of the liquid-crystal layer), but may transmit all the other circularly-polarized light including the right-handed circularly-polarized light having a wavelength not falling within that range as above and the left-handed circularly-polarized light of all wavelengths. In other words, the liquid-crystal film of the case can selectively separate right-handed circularly-polarized light having a specific wavelength from left-handed circularly-polarized light (circular dichroism). From the viewpoint of applications of optical devices, concretely, there are two different cases, (A) 350/nave (nm)<P≦800/nave (nm), or that is, in this case, the circular dichroic wavelength region is in a visible light region; and (B) P<350/nave (nm), or that is, in this case, the circular dichroic wavelength region is in a UV region. In these, nave=(ne2+no2)/2)0.5.
In the case (A) 350/nave (nm)<P≦800/nave (nm), when non-polarized light is introduced into the liquid-crystal film, then the reflected light and the transmitted light are colored in accordance with the wavelength for the circular dichroism. Based on the coloration mode, the liquid-crystal film may be applied to designs for decorative members and to color filters for liquid-crystal display devices. Further, since the reflected light and the transmitted light have a metallic gloss peculiar to them and their colors vary depending on the viewing angle, and since such optical properties of the liquid-crystal film could not be duplicated in ordinary duplicators, the film can be applied to forgery prevention. In addition, based on the circularly-polarized light-separating function thereof, the film can be used for improving the light utilization efficiency in liquid-crystal display devices. For example, there is proposed a constitution of laminating a polarizer with a ¼λ plate and an optically-anisotropic film that expresses a function of separating circularly-polarized light (see Non-Patent Reference 1). In these applications, the film is required to express its circularly-polarized light-separating function in the entire visible light region (wavelength region of from 350 to 750 nm), for which plural layers each having a different pitch may be laminated or the film is so designed that its pitch may continuously vary in the direction of the thickness thereof. The reflection spectrum width Δλ is wider when the birefringence anisotropy (Δn) is larger, from their relational formula, Δλ=Δn×P. The center wavelength λc of the reflection spectrum is computed from its relational formula, λc=nave×P.
Apart from the above, when the same circular polarization-separating function is used and when the range is defined to 700/nave (nm)<P≦1.5/nave (μm), then the liquid-crystal film may be applied to UV or near-IR reflection filters, etc.
In the case (B) P≦350/nave (nm), the refractive index in the visible light region to the plane vertical to the helical axis of the film is represented by ((ne2+no2)/2)0.5, and the refractive index in the visible light region in the direction of the helical axis is equal to no (see Non-Patent Reference 2).
The optically-anisotropic film having such optical characteristics is referred to as a negative C-plate. In a liquid-crystal display device that exhibits black display (dark condition) when the liquid-crystalline molecules having a positive birefringence are oriented vertically to the substrate therein, there occurs no birefringence owing to the orientation of the liquid-crystalline molecules in the normal direction of the display device. Accordingly, in the display device of the type, a remarkably high contrast can be obtained in the normal direction. However, birefringence occurs when the viewing angle is out of alignment with the normal line of the display device and the transmittance in black display (dark condition) increases. Namely, in the display device, the contrast decreases to the viewing angle in the oblique direction. The negative C-plate can compensate the birefringence which occurs when the viewing angle is out of alignment with the normal direction of the liquid crystal orientation in the display device. As a result, the negative C-plate can be an optical compensator suitable for improving the viewing angle characteristics of various display devices such as VA (vertically aligned), TN (twisted nematic), OCB (optically-compensated birefringence) and HAN (hybrid aligned nematic) devices.
At present, compressed polymer films or films of discotic liquid crystals having planar-oriented negative birefringence (see Patent Reference 2) are used for optical compensators. Utilizing polymers of cholesteric liquid crystals of liquid-crystalline molecules having a positive birefringence broadens the latitude in planning refractive index anisotropy and wavelength dispersion. Negative C-plates can be combined with various optical compensation layers.
In optical planning for the respective applications as above, the pitch and Δn are separately controlled.
For all the applications mentioned above, it is desired to develop photopolymerizing cholesteric liquid-crystal compositions, of which the properties before curing are characterized in that they have a nematic phase at room temperature and have a broad nematic phase, they have broad orientation latitude and they are rapidly curable through exposure to UV rays, and of which the properties after curing are characterized in that they have a suitable Δn, they are transparent and they have good heat resistance and moisture resistance.
When compounds are optimized, they must satisfy polymerizability and physical and chemical properties of the resulting polymers, in addition to the above-mentioned optical properties. The physical and chemical properties which the compounds and their polymers must satisfy include the polymerization speed of the compounds, the polymerization degree of the polymers, as well as the transparency, mechanical strength, coatability, solubility, crystallinity, shrinkage, water permeability, water absorbability, vapor permeability, melting point, glass transition point, clear point, heat resistance and chemical resistance thereof.
When an optically-active compound is added to a liquid-crystal compound, then it induces a helical structure (see Patent Reference 3 or 4). The pitch (p) depends on the amount of the optically-active compound added (concentration, c) and the helical twisting power (HTP) thereof. p=HTP−1×c−1. Liquid-crystal compositions having a helical structure can be utilized in various applications. For example, there are mentioned PC (phase-change) display devices, guest-host display devices, TN display devices, STN display devices, SSCT (surface-stabilized cholesteric texture) display devices, PSCT (polymer-stabilized cholesteric texture) display devices, N-type C-plates (negative C-plates), etc.
In all these applications, it is desirable that the amount of the optically-active compound to be added is minimized in order that the compound added does not have any negative influence on the other physical properties such as viscosity and liquid crystallinity of the liquid-crystal compositions. For this, optically-active compounds having a large HTP are desired. In general, optically-active compounds have a low solubility in liquid-crystal compositions, and therefore it is difficult to increase the amount of the compound that may be added to the composition. Accordingly, optically-active compounds having a large HTP are desired.
To applications for polarizers, optical compensators such as N-type C-plates, orientation films, color filters, adhesives, synthetic polymers having mechanical anisotropy, cosmetics, decorations and forgery-preventing devices, optically-anisotropic shaped articles may be utilized. For these, desired are shaped articles that are excellent in point of the polymerization degree of the polymers, as well as the transparency, mechanical strength, coatability, solubility, crystallinity, shrinkage, water permeability, water absorbability, vapor permeability, melting point, glass transition point, clear point, heat resistance and chemical resistance thereof. In addition, the liquid-crystal composition that contains an optically-active compound must be excellent in point of the polymerization speed thereof.    Patent Reference 1: JP-A 8-87008 (U.S. Pat. No. 5,599,478),    Patent Reference 2: JP-A 2002-6138 (U.S. Pat. No. 6,685,998),    Patent Reference 3: British Patent A-2298202,    Patent Reference 4: WO02/28985 pamphlet,    Non-Patent Reference 1: Y. Hisatake et al., Asia Display/IDW '01 LCT8-2,    Non-Patent Reference 2: W. H. de Jeu, Physical Properties of Liquid Crystalline Materials, Gordon and Breach, New York (1980).
An object of the invention is to provide a polymerizing, 1,1′-binaphthalene ring-having liquid-crystalline compound that has a large HTP and good solubility with other liquid-crystal compounds, and to provide a liquid-crystal composition that contains the compound. Another object of the invention is to provide a polymer having many good properties such as transparency, mechanical strength, coatability, solubility, crystallinity, shrinkage, water permeability, water absorbability, vapor permeability, melting point, glass transition point, clear point, heat resistance and chemical resistance, and to provide an optically-anisotropic shaped article formed of the polymer. Still another object of the invention is to provide polarizers, optical compensators, orientation films, color filters, holographic devices, liquid-crystal display devices, adhesives, synthetic polymers having mechanical anisotropy, cosmetics, decorations, forgery-preventing devices, non-linear optical devices and optical memory devices that comprise the polymer.